Method of preparing animal glue



United States Patent 53cc METHOD OF PREPARING AWllViAL GLUE Havard L. Keil, Clarendon Hills, Louis A. Harriman,

Chicago, and Arlan G. Roberts, Dalton, Ill., assignors to Armour andCornpany, Chicago, Ill., a corporation of Hlinois No Drawing. Application February 26, 1953, Serial No. 339,166

Claims. (Cl. 195-6) This application is a continuation-in-part of our copending application United States Serial No. 243,378, filed August 23, 1951.

The present commercial practice for preparing'cattle hide glue involves the following principal steps: 1

1. The cattle hide glue stock is soaked in a saturated lime solution for a period of from 60 to 120 days, depending on the temperature, for the purpose of softening and conditioning the glue stock.

a 2. The conditioned glue stock is then soaked in water at an acidic pH to remove lime and calcium salts including the carbonates.

3. The glue stock is then washed back to approximately a neutral pH value, or neutralized with an alkaline reagent.

4. The conditioned, swollen and neutralized glue stock is then extracted with hot water in a series of cooks at increasing temperatures to obtain the glue.

The reason for this lengthy conditioning process is found in the fact that it is very difiicult to prepare glue from hide glue stock having a high gel strength and a correspondingly high viscosity. By way of contrast, gelatin is easy to prepare. Although gelatin is almost chemically identical with glue, it has such a low viscosity that it has not been acceptable to the trade for adhesive purposes.

An isolated collagen fiber can be easily extracted to obtain glue, but when the collagen fibers are in their natural state within solid pieces of hide stock, it is very difficult to extract the glue. The pieces of hide stock must be opened up or conditioned to make the extraction feasible. 'A long standing problem in the field is how to do this conditioning rapidly without damaging the collagen. The conversion of collagen to glue involves a very slight change, and there is even a dispute as to whether the change can be properly described as a chemical change. It is known that the conversion of collagen to glue does not involve proteolysis in the ordinary sense, i. e., splitting of polypeptide chains.

It has been suggested that the lengthy lime conditioning process might be avoided by employing enzymes to condition the glue stock. However, the use of enzymes for this purpose has not proven practical because they degrade the collagen past the glue stage. Therefore, although there is a manifest need for a shorter process involving less handling of the glue stock, and less chemicals, no process has heretofore been developed which is capable of producing glue of a quality comparable to the high grade glues of commerce.

It is therefore a general object of this invention to provide a new process for preparing animal glue which substantially overcomes the above problems, and makes possible the preparation of high grade animal glue in a greatly 'yeast organisms on the hides to noculate the conditioning medium. This method of procedure is especially good reduced period of time, and also requires less handlingof the glue stock, and less chemicals. It is a further object of this invention to provide a novel process for preparing glue from cattle hide glue stock which achieves the broad object just stated, and at the same time produces high yields or excellent quality glue from the standpoint of gel strength and viscosity. Further objects and advantages will appear as the specification proceeds. This invention is based in part on the accidental discovery that collagen-bearing animal tissues can be rapidly conditioned for glue extraction by subjecting the tissues to the enzymatic action of yeasts and yeast-like microorganisms.

Any collagen-bearing animal tissue can be employed as the starting material in the process of this invention. However, the process realizes its greatest advantage. in

the preparation of hide glue, and therefore hide glue stock, and particularly cattle hide glue stock, is preferably em ployed as the starting material. Cattle hide glue stock is of two principal types. It is salt-cured stock or fresh stock. The salt-cured stock is the trimmings from salt-. cured hides. Fresh stock is mainly the trimmings from fresh hides, and in particular the so-called ears and lips. The principal source of raw material is salt-cured hide trimmings. Hides from freshly slaughtered animals. are cured preparatory to the tanning operation by storing in cellars for a period from 30 to days. The hide cellars are maintained at 'a temperature of about 10 C. andthe hides are stacked in piles with a layer of rock salt between the individual hides. When the curing is cornplete the hides are trimmed, bundled and shipped to the tannery. The scrap pieces trimmed from'the cured hides are then utilized as the raw material for the manufacture of hide glue.

In practicing the process of this invention, the conditioning of the solid pieces of collagenbearing tissue is accomplished by suspending the tissue" in an aqueous acidic rnedium and culturing yeasts or yeastlike organisms in the medium which have a conditioning action on the glue stock. It will be understood, of course, that the aqueous medium should be maintained under pH conditions, temperature conditions, etc., which are known to be favorable to the growth of yeast and yeast-like microorganisms. The particular yeasts which have been found most desirable for this purpose are the socalled wild yeasts of the genus Mycoderma. As a member of the class Fungi Imperfecti, Mycoderma be; longs to the family T orulopsidaceae, which contains other yeast-like genera exhibiting a hide-conditioning action, such as the genus Torulopsis. Although Mycoderma or.- ganisms can be used separately, it is preferred to'employ both Mycoderma and Torulopsis organisms. Apparently a synergistic relation exists between these yeast-like organisms in conditioning hide for glue extraction: In particular, the organism ,Mycodermu (sp.) is believed to soften the keratin layerof the hide as well as the elastin,

sheathes around the collagen fibers by its ability to remove sulphur from cystine, and by so doing an' important 'cross linkage between peptide chains is broken so that the structure is weakened and at thesa'me' time is'o'pened up so that Water may enter. Torulopsis (sp.) is believed to aid in the conditioning of the hides by its ability .to hydrolyzethe fatty tissueipresent in the hide pieces, thus permitting easier penetration of the glue extraction waters "to the inner hide structure.

Both Mycoderma and Torulopsis are ubiquitous .01.-

ganisms, being found in the air, dust, 'etc. :Theseorgan- (isms are also found in quantity on cattle hides. Advantage can be taken of this fact by using the indigenous Patented Sept. 3, 1957 a for salt-cured hide trimmings, since the hide cellars provide excellent conditions for the multiplication of both Mycoderma and Torulopsis, and these organisms are always found to be present in hide cellars. If desired, the aqueous medium can be inoculated with Mycoderrna and Torulopsis organisms, which can be cultured for this purpose, and charged to the conditioning bath in the form ofan active broth. A- convenient source of these yeast-- like organisms is in the so-called hairballs, which are found in quantity at .stoc'kyards. ('Hairballs are matted balls of hair and manure which are cut off the outer portion ofcattle hides.)

1 Other organisms can also be present in the conditionin-gbath, and some have been found to exhibit a synergistic or at least symbiotic effect. In'particular, the true yeasts of the tribe Sacch-aromyceteae, such as Saccharom-yces, have been found to be advantageous for thispurpose. The genus Saccharomyces contains most of the well-known commercial yeasts, such as' bakers yeast, brewers yeast, etc., and contains such specific yeast organisms as S. cerevisiae and S. carlsbergensis. These yeasts apparently stimulate the growth of Mycoderma' and Torulopsis yeasts, thereby accelerating the hide conditioning.

It is desired to maintain the aqueous conditioning medium substantially free of putrifactive bacteria and molds. This can be accomplished in a number of Ways. For exampleg the glue stock can be. sterilized with a germicidal agentibefore it is introduced into the conditioning bath, and precautions can be taken toprevent bacteria and molds from being introduced into the bath. .One sterilizing agent which might be employed for this purpose with particular advantage is hydrogen peroxide, since it. canbe readily. destroyed by the use of catalase after the .sterilization has been achieved. Alternatively, the aqueous conditioning medium can be maintained at a pH sufliciently low to inhibit the growth of bacteria and molds while permitting the growth of the desired yeasts or yeast-like organisms. This technique is described in co pending application United States Serial No. 243,378, cited above.

While the above methods of culturing yeasts and yeastlike organisms and maintaining the medium substantially free of putrifactive bacteria and molds are entirely feasible,..it is preferred toemploy still another method of accomplishing this result in which a selective bactcricide is incorporated in the conditioning medium. It has been discovered that water-soluble silicofiuoride salts are particularly good for. this purpose under the conditions of the process. Sodium, potassium, or ammonium silicofluorides are preferred, but other water-soluble silicofluoride salts can be used, and in particular the alkali metal .silicofiuorides. These salts can he used up to the limit of their. solubility, but with more soluble salts such as sodium silicofluoride, it is preferred to operate with aqueous solutions at about one-half saturation. For example, a..3% aqueoussolution of sodium silicofluoride is aboutone-half saturation.

.The .use of selective bactericides and particularly of silicofluoride salts permits the conditioning to be carried out at higher temperatures .and pHs, thereby accelerating thegrowth'of the desired organisms and shortening the'conditioning time. In general, the conditioning step 'can be satisfactorily carried out at temperatures from .15 to 45 C., and best results are achieved at temperatures ranging from 20 to 40 C. When carrying out the conditioning in the presence of a silicofluoride salt, the pH should be maintained between 3.5 and 6.5 and preferably between 4.0 and 5.0. At pHs below 3.5, the silico- -fiuoride salts have a tendency to inhibit the growth of the yeast'as well as the bacteriaand molds.

During the conditioning step, the pH will tend to vary somewhat, and therefore it is preferred to make periodic adjustments of the pH to maintain it within the specified limits. In making the initial and subsequent pH adjust- 4. merits, various organic and inorganic acids can be employed, such as acetic, nitric, phosphoric, and sulfuric, etc. Of course, it will be understood that the acid employed must not be toxic to the desired organisms. Hydrochloric acid is the reagent of preference.

The time required to complete the conditioning will vary somewhat depending on the particular conditions. It may take from 1 to 21 days to complete the conditioning, although in the preferred process as described herein usually 2 to 3 days are sufficient. The point at which the hide stock has become sufficiently conditioned can be easily determined by visual observation and by simple tests. When the hide is conditioned, it is usually quite soft and can be cut with a fingernail. Both hair and scurf (the outer epidermal layer) can be easily pulled.

The organism-conditioned glue stock can be directly extracted, after neutralization of the acid, with hot water in accordance with conventional practice. However, it is preferable to first plump or swell the glue stock by treating it in an acid bath at a lower pH than in the organism'conditicning. For this swelling step, pHs of from 1.5 to 3.5 give good results, and maximum swelling is achieved at pHs ranging from 2 to 2.5. Hydrochloric acid is preferred as the acidic reagent, although many other acids can be satisfactorily employed, e. g, acetic, nitric, phosphoric, sulfuric, etc. I The temperature in the swelling step is not especially critical, and room temperatures are quite satisfactory (20 to 25 C.). A suitable range temperature for the swelling operation is from 15 to 40 C. In the swelling operation, the Water penetrates the solid pieces of hide in as short a time as 3 hours, and maximum swelling may he achieved in 24 hours. There is some advantage in a longer time of contact of the glue stock with the swelling solution, and therefore it may be desirable to soak the glue stock in the acidified water for periods up to 3 to 4 days. In this way, swelling of from 210 to 225% can be achieved, as compared with swelling of from 150 to 170% in the conventional liming and plu'mping procedures.

The plumped stock can be washed to removethe acid contained therein, and thus brought to a neutral pH, or it can be neutralized with various alkaline reagents such as ammonium hydroxide, sodium hydroxide, sodium carbonate, etc. After neutralization, the glue stock can be extracted with hot water according to conventional pro cedures.

Thetemperatures, cooking times, and ratio of water to solids ca'n all be satisfactorily determined according to the usual practice. For example, the glue stock solids can be covered 'with water and cooked for 3 hours at 65 C; to obtain a glueliquor, which can be subsequently dried or evaporated to obtain the solid glue. The glue stock Zresidue frorn'the first extraction can then be re extracted once at "65 C. and then carried through :a-series of similar extractions at progressively higher tempera- -tures, e. g.,"at 75C., at C., and C.

This invention is illustrated in a number of different specific embodiments 'in the following examples.

Example I Highquality glue can be prepared from collagen-bearing animal tissue according to the following procedure:

The hide trimmings, or other collagen-bearing glue stock, 'is-cov'ered with water and a culture containing .hide is thenlremoved; and after being rinsed in running .water, it is'rca'dy to 'go"into'the-next step,

The rinsed stock is covered withwater and hydrochloric acid added to about pH 2.0. Itisheld at room temperature'and more hydrochloric acid added daily to maintain a-pH between 2.0-2.5. At the end of 2-4 days, the hide is satisfactorily conditioned for glue extraction.

It is possible to use the first step alone. This saves much time and work since the tissue does not receive acid plumping. However, the glue thus obtained is usually of somewhat lower viscosity.

Example 11 Thirteen pounds of fresh cattle hide trimmings were put into-4 gallons of water containing 42 grams of sodium silicofiuoride. A culture of the conditioning microorganisms was added and the mixture held at 35 C. Sufiicient hydrochloric acid was added daily to maintain the pH at about 4.045. At the end of 4 days, the tissue w'aswashed in 'cold water for a few hours and was then subjected to the regular procedure for the extraction of glue, after neutralization. -.Glue extraction consists of covering the stock with water and heating it at 65, 75, 85, 95, and 100 C.

for '3 hours respectively. The glue liquors thus obtained are separately concentrated in vacuo and subsequently dried in a wind tunnel.

Example III Twelve pounds of salted cattle hide scrap were washed in running water overnight to remove salt. The scrap was then put into 4 gallons of water containing 42 grams of sodium silicofluoride. A culture of the conditioning microorganisms was added and the mixture held at 35 C. Sufficient hydrochloric acid was added daily to maintain the pH at about 4.0-4.5. At the end of 3 days, the tissue was washed in cold water for a few hours, after which it was transferred to the second step. 7

The stock was covered with water and 50 cc. of concentrated hydrochloric acid added at A. M. to pH 2.1. At 2:15 P. M. the same day the pH read 2.5, so 35 cc. of the acid was added to pH 2.0. On the following day, the pH was 2.4 at 9 A. M. 50 cc. of the acid was added to reach pH 2.0. On the next (third) day the pH was 2.2 and on the fourth day the same. An equilibrium had thus been attained on the third day of acid treatment, which shows that swelling was at the maximum. The stock was thoroughly conditioned, so itwas vneutralized by water-washing for two days and the glue extracted in the same manner as that described in Exam I Example IV A 45# lot of salted cattle-hide pieces, obtained from the trimmings pile of the hide cellar, was washed for 4 hours in cold running water in order to clean, soften, and partly desalt the material. A tumbler-type washing machine was employed. A one-hour 'wash has been found to be sufi'icient to remove dirt and blood from fresh hide pieces. v

The washed hides were then transferred to a 30-gal. barrel and 225 g. of sodium silicofluoride, equal to 1.11% of the as-received weight of the hide pieces, was added and the barrel filled with warm water. The pH of the mixture was adjusted to 4.0 by addition of hydrochloric acid. Barrel temperature was conveniently maintained at 35-37 C. by use of a Fenwal Thermoswitch, knifetype immersion heater, and electric stirrer to insure circulation. During the three days of this treatment, hydrochloric acid was added intermittently in order to maintain pH at 4.0. A total of 95 cc. of concentrated hydrochloric acid was employed. Lots as large as 80# have .been successfully handled in this same equipment.

Treatment at pH 4.0 in the presence of sodium silicofluoride is, necessary in order to obtain hair loosening and keratin softening. At the end of the first day of this After treatment at pH' 4.0 -for 3, days, the water was changed and stirring and heating were discontinued. The p'H'was adjusted to 2.0 by addition of hydrochloric acid and was maintained at this value for 4 days by intermittent addition of fresh acid. For the 4-day period, a

total of 450 cc. of concentrated hydrochloric acid was thereby diminishing the ash content of the final glue. By

placing a filter screen in the efiluent wash stream it is possibleto collect the freed cattle hair. The hair is light in color, in good condition, and may have a useful market.

Thewashed hides were stored before actual glue cooking in hydrochloric acidsolution at pH 2.0. Storage for extended periods has-no apparent effect on glue qualitysince equilibrium is attained within the 4-day treat-' ment and no additional hydrochloric acid .is absorbed. The conditioned glue stock was then extracted. A sched-' ule of four 3-hour cooks was employed. Cooking temperatures were and boiling.

Hide pieces were placed in a pot and the temperature was quickly elevated by addition of suflicient water at the desired cooking temperature to cover the hide pieces. The cooking pot was maintained at cook temperature by external heating fora 3-hour period. At the completion of the cook, glue liquors were drained, preservative (Dowicide G) was added, the solution was concentrated under vacuum, jellied, and dried either in a heated wind oven or a vacuum oven. A light-colored and frequently transparent dried glue was obtained. At the end of the fourth cook, the residue, which still appeared to contain some potential glue-forming material, was dried for weighing in the wind oven.

In a series of replicate runs following the specific procedure set. out above, the average yield of glue was around 20% on an as-received basis. The average jell strength of the glue was around 440 grams, and the average viscosity was millipoises.

Example V Ten pounds of trimmings from salt-cured cattle hides were washed in running water for 24 hours to remove the salt and dirt- The washed hide pieces were covered with 5 gallons of water and 50 ml. of concentrated hydrochloric acid was added. The pH after the addition of the acid was 2.3. Periodically the pH was determined and sufficient acid added to maintain the pH between 2.0 and 2.5. After 5 days the surface of the bath was covered with a wrinkled gray film and the hide hair slipped easily. After the 21st day of conditioning the hide was removed from the bath and weighed up at 7304 grams. v The pieces were covered with water and 3% or 219 ml. of concentrated ammonium hydroxide was stirred into the lot. The stock remained in the ammonium hytreatment, hair could be pulled from many of the pieces,

and by the conclusion of the third day, much loose hair was floating in the mixture.

droxide solution for 24 hours and was then removed for 'glue cooking operations.

Example V1 Thirty pounds f alt d; hide r p w Wa hed. i running water for 24 hours to remove the. salt, and dirt. The washed hide, scraps were covered with 15 gallons of water and 150, ml. of concentrated hydrochloric acid was added. The. pH after the addition of acid was 2.0. Additional acid was added as necessary to maintain the pH. between 2.0 and 2.5.. After 26. days, some of the hide pieces were removed from the bath and weighed up at 11,579 grams. These pieces were then covered with water and 3% or 350 ml. of ammonium hydroxide was stirred into the, lot After.2,4 hours the stock was removed and glue extractions were made following the procedure of Example V. The yield of glue was calculated as 24.9% basedlon an as-received basis. The average jell strength was 317 grams and the average viscosity 135 millipoises.

Example VII The remaining portion of the hide pieces from Example VI were allowed to remain in the conditioning h for a total of. 68 ays.- Following he conditioning p ra the stock was cook d f r glue extra i e g u tained was of, high quality and the viscosity values were not adversely affected by the prolonged conditioning treatment. 7

Example VIII One hundred pounds of salted cattle hide scrap was washed in running water for 24 hours to remove salt and dirt. The washed skins were covered with water and sutlicient hydrochloric acid added to maintain a pH of 2.5, One pound of bakers yeast was added and the lot allowed to stand for 14 days at room temperature.

At the end of this time the stock was thoroughly conditioned as evidenced by a weak epidermal layer which could be cut by the thumb nail. The stock was next rinsed and weighed. This weight, due to water imbibition, was 225 pounds which denotes a 125% weight increase. The lot was covered with water and 3% or 6.75 pounds of ammonium hydroxide was added and allowed to stand for 18 hours to neutralize. Glue was extracted by the usual procedure.

While in the foregoing specification this invention has been described in considerable detail and a number of specific embodiments have been set forth, it will be apparent to those skilled in the art that many of the specific details and embodiments can be varied Widely without departing from the broad idea of the invention.

We claim:

1- 1. a eth o preparing m l glu the st ps f subjecting collagen-bearing animal tissue to reproducing 'yeast microorganisms of the genus Mycoderma indigenous tocattle hides, while maintaining said animal tissue substantially free from putrefactive bacteria and molds, and

thereafter extracting glue from said collagen-bearing tissue.

2. In a method of preparing animal glue, the steps of conditioning collagen-bearing animal tissue, in an aqueous acidic medium with the enzymatic conditioning action of yeast microorganisms both of the genus Mycoderma and the genus Torulopsis indigenous to cattle hides, under conditions favorable to the multiplication of said yeast organisms while maintaining said aqueous acidic medium substantially free from putrefactive bacteria and molds, and thereafter extracting glue from the conditioned animal tissue.

3. The method of claim 2 in which said collagenbearing animal tissue is cattle hide glue stock.

4. The method of claim 2 in which said collagenbearing animal tissue is salt-cured cattle hide trimmings. 5. In a method of preparing animal glue, steps of com ditioning collagen-bearing animal tissues in an aqueous acidic medium with viable yeast microorganisms both of the u y de ma and the genus. Tqr lops s i digenous to cattle hides and a yeast microorganism of the group consisting of Sacdhqromyces cer'evesiae and Srzcclmromyces carlsbergensis, under conditions favorable to the multiplication of said yeast microorganisms while maintaining said aqueous acidic medium substantially free from putrefactive bacteria and molds, and thereafter subjecting the conditioned tissue to a hot Water extraction to obtain the glue.

6. In a method of preparing animal glue, the steps of conditioning in an aqueous acidic medium salt-cured cattle hide trimmings, having disposed thereon viable yeast organisms of the genus Mycoderma indigenous to cattle hides, under conditions favorable to the multiplication of said yeast organisms while maintaining said aqueous acidic medium substantially free from putrefactive bacteria and molds, and thereafter extracting glue from the conditioned hide trimmings.

7. In a method of preparing animal glue, the steps of conditioning collagen-bearing animal tissue in an aqueous medium having a pH of from 3.5 to 6.5 with yeast microorganisms of the genus Mycoderma indigenous to cattle hides, under conditions favorable to the multiplication of said yeast organisms, while contacting said aqueous medium with a water-soluble silicofiuoride salt to maintain said medium substantially free from putrefactive bacteria and molds, and thereafter extracting glue from the conditioned animal tissue.

8. Ina method of preparing animal glue, the steps of conditioning collagen-bearing animal tissue in an aqueous medium having a pH of from 4.0 to 5.0 at a temperature of from 15 to 45 C. with yeast organisms both of the "genus Mycoderma and the genus Torulopsis indigenous to cattle hides, under conditions favorable to the multiplication of said yeast organisms, while contacting said aqueous medium with a water-soluble silicofiuoride salt to maintain said medium substantially free from putr efactive bacteria and molds, and thereafter extracting glue from't-he conditioned animal tissue.

9, The method of claim 8 in which said water-soluble silicofiuoride salt is selected from the group consisting of alkali metal silicofluorides and ammonium silicofiuoride.

10. In a method of preparing animal glue, the steps of'conditioning saltcured cattle hide trimmings in an aqueous acidic medium having a pH of at least 3.5 with yeast organisms both of the genus Mycoderma and the genus Torulopsis indigenous to cattle hides, under conditions favorable to the multiplication of said yeast organisms while maintaining said aqueous acidic medium bst ntially fre r m pu ref i e ac i d mol hen soaking t e c nditi ne id trimm g in w r acidified to a PH of from 1.5 to 3.5 to swell said hide tri ings, and thereafter extracting glue from the con-v ditioned, acid-swollen hid trimming Ref en e Ci in t e fi e of i pa n UNITED STATES PATENTS 1,405,741 Rohm Feb. 7, 1922 2,515,055 Rohm Sept. 17, 1940 FOREIGN PATENTS 2,879 Great Britain of 1917 104,181 Great Britain 1917 OTHER REFERENCES Smyth et al.: Industrial Microbiology, 1930, Williams and Wilkins, Bait, Md., pages -126.

Sumner et al.: The Enzymes, Academic Press Inc. PubQ, New York. .1952, pages 1317-1318. Lodder: The Yeasts, Interscience Pub. Inc., New York, pages 69.9, 700, 708 to 710.

i i ii 

1. IN A METHOD OF PREPARING ANIMAL GLUE, THE STEPS OF SUBJECTING COLLAGEN-BEARING ANIMAL TISSUE TO REPRODUCING YEAST MICROORGANISMS OF THE GENUS MYCODERMA INDIGENOUS TO CATTLE HIDES, WHILE MAINTAINING SAID ANIMAL TISSUE SUBSTANTIALLY FREE FROM PUTREFACTIVE BACTERIA AND MOLDS, AND THEREAFTER EXTRACTING GLUE FROM SAID COLLAGEN-BEARING TISSUE. 